阅读说明：本技术 一种改善t91无缝钢管综合力学性能的生产方法 (Production method for improving comprehensive mechanical property of T91 seamless steel tube ) 是由 胡静 周烨晖 姚经松 缪一新 李和林 于 2020-07-23 设计创作，主要内容包括：本发明属于金属材料改性技术领域,具体涉及一种改善T91无缝钢管综合力学性能的方法,适当降低第一道次轧制变形量,使第一道次轧制后钢管硬度满足第二道次轧制的要求,实现连续两道次冷轧,即两道次轧制之间不进行通常的退火处理、只进行磷化处理。之后对轧制态钢管进行优化工艺的淬火+回火处理,从而获得具有优良综合力学性能的T91成品管。该方法使第一道次轧制获得的高密度位错得到保留,第二道次轧制进一步提高位错密度、细化晶粒。淬火使显微组织进一步细化,回火使T91钢中形成弥散分布的合金碳/氮化物,通过弥散强化进一步提高无缝钢管的强度和硬度,同时塑性没有明显下降。(The invention belongs to the technical field of metal material modification, and particularly relates to a method for improving comprehensive mechanical properties of a T91 seamless steel tube. And then quenching and tempering the rolled steel pipe in an optimized process to obtain a T91 finished pipe with excellent comprehensive mechanical properties. The method enables high-density dislocation obtained by the first pass of rolling to be reserved, and the second pass of rolling further improves the dislocation density and refines grains. Quenching further refines the microstructure, tempering forms alloy carbon/nitride in the T91 steel in a dispersed manner, further improves the strength and the hardness of the seamless steel pipe through dispersion strengthening, and simultaneously does not obviously reduce the plasticity.)

1. A production method for improving comprehensive mechanical properties of a T91 seamless steel pipe is characterized by comprising the following steps: the method comprises the following process steps:

(1) selecting a hot-rolled and annealed T91 seamless steel tube as a research object;

(2) carrying out cold rolling twice on the steel pipe, carrying out phosphating treatment in the middle of the cold rolling twice, and carrying out deoiling treatment on the steel pipe after rolling;

(3) and quenching and tempering the rolled steel pipe to obtain the finished T91 seamless steel pipe.

2. The production method for improving the comprehensive mechanical property of the T91 seamless steel tube according to claim 1, wherein the production method comprises the following steps: the specification of the steel pipe in the step (1) is phi 82mm multiplied by 8.5 mm.

3. The production method for improving the comprehensive mechanical property of the T91 seamless steel tube according to claim 1, wherein the production method comprises the following steps: the cold rolling process in the step (2) comprises the following steps: the first-pass rolling deformation is 40-50%; the rolling deformation of the second pass is 22-26%, annealing is not carried out between the two passes, and the total deformation of the cold rolling is 60-65%.

4. The production method for improving the comprehensive mechanical property of the T91 seamless steel tube according to claim 1, wherein the production method comprises the following steps: the phosphating treatment in the step (2) comprises the following steps: putting the steel pipe into a phosphating solution at the temperature of 50-70 ℃ for soaking for 30-40 min, wherein the mass ratio of the phosphating solution to water is 1: 10; the degreasing treatment comprises the steps of cleaning the surface and the inner wall of a rolled steel pipe by using an alkaline metal degreasing and degreasing powder aqueous solution, and removing grease and oil stains on the surface and the inner wall, wherein the mass ratio of degreasing powder to water is 1: 5.

5. the production method for improving the comprehensive mechanical property of the T91 seamless steel tube according to claim 1, wherein the production method comprises the following steps: and (3) preheating twice before quenching, wherein the primary preheating temperature is 500-600 ℃, the heat preservation time is 10min, the secondary preheating temperature is 800-850 ℃, and the heat preservation time is 10 min.

6. The production method for improving the comprehensive mechanical property of the T91 seamless steel tube according to claim 5, wherein the production method comprises the following steps: the quenching process comprises the following steps: the temperature is 1040-1060 ℃, the heat preservation time is 10min, and the cooling mode is air cooling; the tempering process comprises the following steps: the temperature is 760-780 ℃, the heat preservation time is 60min, and the cooling mode is air cooling.

Technical Field

The invention belongs to the technical field of metal material modification, and particularly relates to a production method for improving comprehensive mechanical properties of a T91 seamless tube.

Background

The T91 steel has high strength, good plasticity and good oxidation resistance and corrosion resistance, and can be used for manufacturing heated surface pipes such as a reheater and a superheater of a high-pressure boiler with a metal wall temperature of less than 625 ℃ and steam guide pipes with a metal wall temperature of less than or equal to 600 ℃ and the like. At present, T91 seamless steel tubes have gradually occupied the main position of manufacturing large-capacity subcritical and supercritical power station boilers in China.

The tensile strength of a finished pipe obtained by the traditional T91 production process is 680-700 MPa, the yield strength is 520-540 MPa, the hardness is 200 HBW-220 HBW, and the service conditions of certain specific environments such as Supercritical (SC) and Ultra Supercritical (USC) unit pipes and the like are still difficult to meet, wherein the service conditions include that the steam pressure is more than or equal to 25MPa, the steam temperature is more than or equal to 580 ℃, the normal-temperature tensile strength is required to be more than or equal to 750MPa, the yield strength is more than or equal to 580MPa, and the hardness is about 250 HBW. Meanwhile, the traditional T91 production process has a long period, and cannot achieve the effects of energy conservation and high efficiency.

Disclosure of Invention

The technical problem to be solved by the invention is as follows: based on the technical problems, the invention provides a production technology and a process method for improving the comprehensive mechanical property of a T91 seamless steel tube.

The technical scheme adopted by the invention for solving the technical problems is as follows: a production technology and a process method for improving comprehensive mechanical properties of a T91 seamless tube comprise the following steps:

(1) the hot-rolled and annealed T91 seamless steel pipe is selected as a research object.

The specification of the steel tube is phi 82mm multiplied by 8.5 mm.

(2) Performing two-pass cold rolling on an LG325-H two-roll cold rolling mill, performing only phosphating treatment without annealing in the middle of the two-pass cold rolling, and performing deoiling treatment on the steel pipe after rolling;

the phosphating treatment comprises the following steps: putting the steel pipe into a phosphating solution at the temperature of 50-70 ℃ for soaking for 30-40 min, wherein the mass ratio of the phosphating solution to water is 1: 10.

the cold rolling process comprises the following steps: the total cold rolling deformation is 60-65%, and the first-pass rolling deformation is 40-50%; the rolling deformation of the second pass is 22-26%, and annealing is not carried out between the two passes.

Deoiling treatment: cleaning the surface and the inner wall of a rolled steel pipe by using an alkaline metal degreasing and degreasing powder aqueous solution, and removing grease and oil stains on the surface and the inner wall, wherein the mass ratio of degreasing powder to water is 1: 5.

(3) and quenching and tempering the rolled steel pipe to obtain a finished pipe.

Preheating twice before quenching: the primary preheating temperature is 500-600 ℃, the heat preservation time is 10min, the secondary preheating temperature is 800-850 ℃, and the heat preservation time is 10 min.

The quenching process comprises the following steps: the temperature is 1040-1060 ℃, the heat preservation time is 10min, and the cooling mode is air cooling. The tempering process comprises the following steps: the temperature is 760-780 ℃, the heat preservation time is 60min, and the cooling mode is air cooling.

(4) And sampling, detecting and analyzing the finished pipe. The test analysis specifically comprises:

1) observing the microscopic structure of the section by adopting an optical metallographic microscope;

2) performing hardness test analysis by using a Brinell hardness tester;

3) and (4) carrying out related mechanical property test analysis by adopting a multifunctional tensile testing machine.

The invention idea is as follows:

in the cold rolling process, dislocations are continuously formed along with the progress of plastic deformation, and the dislocation density is continuously increased, causing work hardening. The conventional cold rolling process needs annealing in the middle of two-pass rolling, and in the annealing process, recrystallization occurs, the dislocation density is reduced, the strength and the hardness of the steel pipe are reduced, the plasticity is improved, and the next-pass rolling is facilitated. The invention omits the intermediate annealing step, adopts proper deformation amount through the first pass rolling, and directly performs the second pass rolling after only performing phosphating treatment without annealing between the two passes of rolling under the condition that the hardness of the steel pipe meets the requirement of the second pass rolling, thereby keeping the high-density dislocation obtained by the first pass rolling, further improving the dislocation density and refining the crystal grains by performing the second pass rolling on the basis, and obviously improving the strength and the hardness of the steel pipe.

On the basis, the T91 seamless tube is subjected to quenching treatment, based on the inheritance of the structure in the heat treatment process, austenite grains which are finer than those of the traditional method can be obtained in the process of austenitizing by quenching and heating, austenite is converted into martensite with fine grains in the cooling process, and the strength of the T91 seamless tube is improved by fine grain strengthening. In the tempering process, carbon/nitride forming elements such as V, Nb and Cr in the T91 steel and C/N form alloy carbon/nitride, the alloy carbon/nitride is preferentially dispersed and precipitated at crystal defects such as dislocation, grain boundary and the like, and fine dispersed carbon/nitride can effectively prevent dislocation movement, so that the strength of the T91 steel seamless tube is greatly improved.

The invention has the beneficial effects that:

(1) the invention optimizes the cold rolling process, saves the intermediate annealing step of the traditional cold rolling process, and retains the high-density dislocation obtained by the first rolling, thereby further refining the crystal grains and improving the strength and the hardness of the T91 seamless tube. Meanwhile, the annealing process is omitted, so that the logistics process can be simplified, the production efficiency is improved, and the production cost is reduced.

(2) Compared with the conventional one-time preheating, the method provided by the invention has the advantages that the final heat treatment process is optimized, and the method is used for carrying out twice preheating before quenching, so that the deformation and cracking tendency of the T91 seamless tube in the quenching and heating process can be reduced, the heat preservation time of the T91 seamless tube in the quenching and heating process is shortened, the oxidation and decarburization of the T91 seamless tube are reduced or avoided, the burning loss is reduced, and the furnace temperature stability can be accurately controlled.

The invention is further described below with reference to the accompanying drawings.

Drawings

FIG. 1 is the structure of the finished tube obtained in example 1;

FIG. 2 is the structure of the finished tube obtained in example 2;

FIG. 3 is the structure of the finished tube obtained in example 3;

FIG. 4 is the structure of the finished tube obtained in example 4;

FIG. 5 is a structure of a finished tube obtained in comparative example 1;

FIG. 6 is a sample of the finished tube crush test obtained in example 1;

FIG. 7 is a sample of the finished tube crush test obtained in example 2;

FIG. 8 is a sample of the finished tube crush test obtained in example 3;

FIG. 9 is a sample of the finished tube crush test obtained in example 4;

FIG. 10 shows macrocracks in the crush test of the finished tube obtained in comparative example 2.

Detailed Description

The present invention is further described below with reference to examples, but is not limited thereto.